(1) Field of the Invention
The present invention relates to an optical compensated bend (OCB) mode liquid crystal display (LCD), and more specifically to an OCB mode LCD including a display panel that is capable of accelerating the transition of liquid crystal molecules from splay alignment into bend alignment.
(2) Description of the Prior Art
Liquid crystal displays (LCDs) are compact in size, lightweight, in addition to low power consumption and lower radiation. Due to these meritorious features, LCDs are widely used in personal digital assistants (PDA), notebook computers, digital cameras, video cams, mobile phones, and many other electronic devices. The manufacturers worldwide have devoted themselves to further research and thus improve the materials, processes and equipments. The display qualities of LCDs are accordingly and largely promoted while the cost goes down day-by-day, which, in turn causes a wider use of LCD.
In order to improve the response speed of the liquid crystal molecules and to widen the viewing angle of the display panel, researches related to the material characteristics of the liquid crystal molecules are conducted. Presently, three methods are proposed, namely: (1) the vertical alignment liquid crystal mode; (2) low-viscosity liquid crystal molecules; and (3) the optically compensated bend (OCB) mode.
With the vertical alignment mode, the liquid crystal molecules align with the alignment film and change their orientation rapidly into the vertical direction when a voltage is applied to the pixel electrode. Research conducted on the low-viscosity liquid crystal material indicates that the response time is directly related to the viscosity of the liquid crystal molecules. Shorter response time can be obtained with low-viscosity liquid crystal molecules.
In the OCB mode LCD, the liquid crystal molecules near the upper and lower glass substrates are oriented in parallel directions while the liquid crystal molecules therebetween in the liquid crystal layer are not twisted but are operated in the bent alignment state with respect to a vertical plane. Such type of bent alignment can result in double refraction of the light. A biaxial retardation film is generally used to compensate the axial phase difference so as to overcome the restricted viewing angle caused by the parallel alignment of the liquid crystal molecules on the boundaries. In addition, the liquid crystal molecules in the OCB mode require fast response time of 1-10 ms to switch between dark and bright state operation when compared to the liquid crystal molecules of the TN (twisted nematic) mode which require a response time of about 50 ms.
Note that, though the OCB mode LCD has the aforesaid advantages, there still exist some disadvantages, such as the requirement of a longer warming-up time in order to perform the transition of the liquid crystal molecules in the liquid crystal layer from the splay alignment into the bend alignment. In the presently available OCB mode of LCD, a high voltage is generally applied to the liquid crystal layer in order to quicken the transition of the liquid crystal molecules of the liquid crystal layer from the splay alignment into the bend alignment. FIGS. 1A and 1B respectively show the liquid crystal molecules 10 in the splay alignment state and the bend alignment state. When a predetermined voltage is applied on the common electrode 12 and the pixel electrode 14, the molecules 10 of FIG. 1A in the splay alignment are changed into the bent alignment of FIG. 1B after being twisted.
In order to accelerate the transition of the molecules 10 from the splay alignment into the OCB mode, a high voltage is usually applied between the common and pixel electrodes 12, 14 and to the liquid crystal layer therebetween. However, such method cannot uniformly and rapidly transit all the molecules into the required bent mode. Under this condition, the display panel of the LCD is unable to display the images in the normal condition.
In order to form a larger voltage difference between the common electrode 14 and the pixel electrode 12, the design of the driver chip for the display panel have to be altered, or, the design of the pixel pattern have to be modified. However, these result in extra production cost. Therefore, the manufacturers are in the trend to produce an LCD having a display panel that is capable of accelerating the transition of the molecules from the splay alignment into the bent alignment.